My long-range goal is to understand the mechanism of cytokinesis in enough detail to make useful mathematical model of the process that can predict the results of future experiments. To address my goal during the next five years, we will combine complementary cellular, biochemical, genetic and modeling strategies with three specific aims. Aim 1. Characterize how cytokinesis-organizing centers called nodes associate with the cell cortex and how node proteins (including Blt1p, anillin Mid1p, Myo2p, F-BAR Cdc15p, formin Cdc12p and IQ-GAP Rng2p) interact during interphase and cytokinesis. This ambitious project combines biochemical and biophysical characterization of each of these proteins and their various interactions with live cell fluorescence microscopy and super-resolution fluorescence microscopy to characterize how these proteins function in cells. Aim 2. Test the search, capture, pull and release hypothesis for contractile ring assembly to learn how precursor nodes transform into a contractile rings. Aim 3. Document how the protein components of the contractile ring disperse during ring constriction and to discover the molecular mechanisms controlling the process. The first two projects emphasize the top of the cytokinesis pathway, because I believe that understanding how a cell assembles a contractile ring is the key to understanding the rest of the process. My reason for this belief is that virtually all of the proteins in the contractile ring organizing centers are retained in the mature contractile ring, so it is logical that the pathway of assembly determines the architecture and operations of mature and constricting rings. The third project continues our effort to understand the terminal function of the contractile ring.